The present invention is directed to welding and, more particularly, to a method and system of aluminum welding without preheating of a workpiece. The invention is particularly applicable with pulsed spray transfer welding.
Gas Metal Arc Welding (GMAW), also referred to Metal Inert Gas (MIG) welding, combines the techniques and advantages of Tungsten Inert Gas (TIG) welding's inert gas shielding with a continuous, consumable wire electrode that is delivered to a weld by a wire feeder. An electrical arc is created between the continuous, consumable wire electrode and the workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. Gas Metal Arc Welding is a relatively simple process that allows an operator to concentrate on arc control. Gas Metal Arc Welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in GMAW may be much higher than those typically associated with either Gas Tungsten Arc Welding (GTAW), also referred to as TIG welding, or Shielded Metal Arc Welding (SMAW), also referred to as stick welding, thereby making GMAW an efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The GMAW process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of GMAW welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required.
Gas Metal Arc Welding can be carried using a number of different transfer modes, such as short circuit transfer, globular transfer, spray transfer, and pulse spray transfer. While each transfer mode may be advantageous for a given application, GMAW using pulse spray transfer (GMAW-P) is particularly advantageous for aluminum welding. Specifically, GMAW-P produces relatively little spatter and may be carried in a number of welding positions. Moreover, by adjusting peak amperage, background amperage, pulse width, pulses per second, and other variables, an operator can adaptively control the GMAW-P process to fit a given application that may not be possible with short circuit transfer, globular transfer, or spray transfer.
As referenced above, GMAW-P is often a preferred welding technique for aluminum welding. A drawback of GMAW-P with aluminum, however, is that customarily the workpiece to be weld must be preheated. Without preheating of the workpiece, it is not uncommon for a “rope-y” weld bead that lays across the weld joint to be formed. This undesirable weld joint is a result of the heat at the weld during start-up of the welding process being insufficient to melt the aluminum electrode and the workpiece into a molten pool. That is, while aluminum has a relatively low melting point, aluminum also has a relatively low resistivity. As a result, when current passes through the aluminum electrode upon formation of an arc between the electrode and the workpiece, relatively little heat when compared to steel is generated. This lack of heat generation must be compensated for to avoid the “rope-y” weld joint referenced above. Generally, the workpiece is preheated such that the preheated temperature coupled with the heat generated at the weld is sufficient to properly melt the electrode and workpiece into a molten pool such that an integrated and structurally sound joint is formed with the workpiece. As can be appreciated, preheating adds to the time, cost, and complexity of the GMAW-P with aluminum process.
One proposed solution to preheating the workpiece when aluminum welding is arbitrarily increasing the power output of the power source during startup of the welding process. In this regard, more power is initially available at the weld resulting in greater heat production. This additional heat is sufficient to create a molten pool of consumable and workpiece for sound weld joint. Moreover, the startup weld pool generates enough heat to sufficiently heat the workpiece such that once power levels are reduced to post-startup levels; the workpiece is heated to a temperature that allows the workpiece to melt during welding in a conventional manner. Thus, after expiration of startup, the power source immediately returns to operate according to user-defined settings.
A drawback of this solution is that the initial or startup power levels are pre-set and thus independent of the user-defined parameters of the welding process. For example, the proposed solution ignores the user-desired weld wire feed speed when setting the startup wire feed speed. That is, in this example, the startup wire feed speed is independent and not proportional to the user-identified and desired weld wire feed speed. This independence of wire feed speed also extends to other operating parameters of the welding process including peak amperage, background amperage, pulse width, pulse frequency, arc length, and the like. As a result, the abrupt changeover from the startup operating parameters to the post-startup parameters can negatively affect the quality of the weld. Moreover, since the desired user parameters are not considered, the preset startup operating parameters may not be optimum for the given application. For example, the startup parameters may ignore the gauge of the aluminum wire feed.
It would therefore be desirable to have a method and system of aluminum GMAW-P that does not require preheating of a workpiece and considers user-desired weld operating parameters when auto-determining optimum startup operating parameters.